PT  - JOURNAL ARTICLE
AU  - Mei Chen
AU  - Barbara LeDuc
AU  - Stephen Kerr
AU  - David Howe
AU  - David A. Williams
TI  - Identification of Human UGT2B7 as the Major Isoform Involved in the <em>O</em>-Glucuronidation of Chloramphenicol
AID  - 10.1124/dmd.109.029900
DP  - 2010 Mar 01
TA  - Drug Metabolism and Disposition
PG  - 368--375
VI  - 38
IP  - 3
4099  - http://dmd.aspetjournals.org/content/38/3/368.short
4100  - http://dmd.aspetjournals.org/content/38/3/368.full
SO  - Drug Metab Dispos2010 Mar 01; 38
AB  - Chloramphenicol (CP), a broad spectrum antibiotic, is eliminated in humans by glucuronidation. The primary UGT enzymes responsible for CP O-glucuronidation remain unidentified. We have previously identified the 3-O-CP (major) and 1-O-CP (minor) glucuronides by β-glucuronidase hydrolysis, liquid chromatography-tandem mass spectrometry, and 1D/2D H NMR. Reaction phenotyping for the glucuronidation of CP with 12 expressed human liver UGT isoforms has identified UGT2B7 as having the highest activity for 3-O- and 1-O-CP glucuronidation with minor contributions from UGT1A6 and UGT1A9. The kinetics of CP 3-O-glucuronidation by pooled human liver microsomes (HLMs) exhibited biphasic Michaelis-Menten kinetics with the apparent high-affinity Km1 and low-affinity Km2 values of 46.0 and 1027 μM, whereas expressed UGT2B7 exhibited Michaelis-Menten kinetics with the apparent Km value of 109.1 μM. The formation of 1-O-CP glucuronide by pooled HLM and expressed UGT2B7 exhibited substrate inhibition kinetics with apparent Km values of 408.2 and 115.0 μM, respectively. Azidothymidine (AZT) and hyodeoxycholic acid (substrates of UGT2B7) inhibited 3-O- and 1-O-CP glucuronidation in pooled HLMs. In 10 donor HLM preparations, both CP 3-O- and CP 1-O-glucuronidation showed a significant correlation with AZT glucuronidation (UGT2B7) (rs = 0.85 and rs = 0.83, respectively) at 30 μM CP, whereas no significant correlation was observed between CP 3-O-glucuronidation and serotonin glucuronidation (UGT1A6) or propofol glucuronidation (UGT1A9) at this CP concentration. These results suggest that UGT2B7 is the primary human hepatic UDP-glucuronosyltransferase isoform catalyzing 3-O- and 1-O-CP glucuronidation with minor contributions from UGT1A6 and UGT1A9. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics